Volume 16, Issue 2,
March 2010

The post-Congress issue of our journal is very much a "mixed bag" of excellent articles, comprising the winning prize entries from the SASA 2010 congress, refresher course texts that were not published in our congress edition, as well as some very interesting peer reviewed case reports.

Methods : Pharmacokinetic-pharmacodynamic simulations were used to estimate the time course of morphine effect-site concentrations in an "average" 59 kg female, and to calculate the degree of resulting respiratory depression.
Results : Morphine effect-site concentrations approached dangerous levels for respiratory depression and persisted for hours, while plasma concentrations were undectectably low.
Discussion : Court testimony indicates that additional factors contributed to the patient's demise. Respiratory depression was potentiated by pain relief following quinsy tonsillectomy, and by falling asleep. The airway was obstructed, as witnessed both by nurses and a fellow patient. In addition, nursing staff failed to recognise that snoring can indicate a dangerously obstructed airway.
Conclusions : Dangerous respiratory depression often goes unrecognised in surgical wards. Strategies for improved safety include education of nursing and other staff regarding the following aspects of respiratory depression : (i) recognition of delayed and prolonged respiratory depression; (ii) noisy breathing indicates obstructed breathing; (iii) respiratory rate is an unreliable monitor of respiratory depression; iv) training in airway management should be compulsory; (v) sleeping patients should be administered oxygen, and pulse oximetry monitoring should be done (especially at night); (vi) more local anaesthesia should be administered for postoperative pain; (vii) combination analgesic therapy (NSAIDs, paracetamol, ketamine, dexmedetomidine, gabapentin) should be utilised to reduce morphine requirements; (viii) high risk patients (e.g. elderly, obese, sleep-apnoea syndrome) should be identified; (ix) sedation scores should be recorded to detect obtunded patients. Morphine plasma concentrations do not reflect pharmacological activity.

Background : A protocol has been devised in which a 20ml mixture of hyperbaric bupivacaine and fentanyl is prepared in a multi-dose syringe, from which aliquots are withdrawn into individual sterile syringes for use in spinal anaesthesia. The risk of microbial contamination of these multi-dose syringes is unknown and this study was designed to assess such risk.
Methods : In this pilot study, each syringe was prepared using non-aseptic technique to contain a mixture comprising fentanyl 10 µg.ml-1, bupivacaine 4mg.ml-1 and dextrose 64mg.ml-1, with a total volume of 20ml. Syringes were then allocated to pairs. Aliquots were withdrawn hourly from one syringe of each pair for a twelve-hour study period, whilst the other syringe was sampled only at the beginning and end of the same period. All aliquots were withdrawn using standard aseptic technique in an operating theatre environment. For each syringe pair, both samples from the control syringe and four of the samples from the multi-dose syringe were submitted for microbiological culture.
Results : Of the 120 samples taken, one sample was excluded. Of the remaining 119 samples submitted for microbiological investigation, only one yielded growth. This sample had been taken from a multi-dose syringe at the beginning of the study period. Subsequent samples withdrawn from the same syringe were found to be sterile. The organism which had been cultured from this sample was Staphylococcus aureus.
Conclusion : It is possible that the culture medium which yielded the microbial growth was contaminated, which would explain why subsequent samples from the same syringe yielded no microbial growth. Alternatively, bupivacaine is known to be strongly antimicrobial against some pathogens and it is possible that there may have been initial contamination of the syringe by S. aureus, which was inhibited by the bupivacaine to produce subsequent sterile samples. Whilst this may suggest that the use of multi-dose syringes for spinal anaesthesia could be safe, in light of the inconclusive result, further investigation is warranted.

Nitrous oxide (N2O) has been a part of anaesthetic practice for over 150 years. During this time, its reputation has seesawed. Today, anaesthetic opinion seems to have swung away from its use. To ascertain whether this is based on sound scientific principles, or can be ascribed to a shift in "medical fashion", a Pubmed search for all articles containing the terms "nitrous oxide" and "anaesthesia" was conducted for the period 2004 to 2009. Relevant articles were selected and supplemented with appropriate articles from their references. This three-part series thus reviews the current knowledge of nitrous oxide. In this, the first article of the series, the history and basic science are reviewed. The focus is on the latest knowledge regarding mechanisms of action and possible pathophysiological mechanisms, and the clinical relevance thereof. New considerations regarding preoperative assessment and premedication are also presented. The remainder of the series will deal with the clinical controversies surrounding nitrous oxide, analyse claimed risks and benefits, and discuss its role in 2010.

As has been alluded to in the first part of this series, nitrous oxide (N2O) is not the known quantity many of us think it is. It appears to be becoming "scientific fashion" among many anaesthetists to view nitrous oxide as an "anaesthetic untouchable" or, at best, a "second rate citizen".

Mild intra-operative hypotension (IOH) in children is not usually a cause for concern. However, what is normal, and how low is low? Some studies in adults have shown that IOH is associated with increased mortality. A study of adult patients by Bijker et al showed no causal relationship between mortality and IOH, but the definitionof IOH was problematic. However, there was a trend towards increased mortality in the elderly with sustained IOH. In a population of healthy children, is brief, mild IOH even an issue when there is seemingly no causal relationship in elderly vascular patients? Probably not but, ethically, this study could never be performed. Thousands of children have undergone anaesthesia and have been subjected to episodes of mild brief IOH without any adverse outcomes.

A 55-year-old man diagnosed with ankylosing spondylitis presented for inguinal hernia repair. The patient was found to have limited neck movement, thoracic kyphosis and restrictive lung disease. Surgery was performed under hernia block, which was inadequate. General anaesthesia was then administered and airway patency was maintained with an endotracheal tube used as a nasopharyngeal airway.

A three feet two inch (96 cm) tall achondroplastic patient with urothelial cell carcinoma involving renal pelvis was scheduled for a radical nephrectomy. Radial artery cannulation and central venous access were secured in the pre-induction period. After induction, the airway was secured using a flexible fibreoptic scope. General anaesthesia was maintained with oxygen-nitrous-oxide and continuous propofol infusion. The total duration of anaesthesia was three hours and 50 minutes. To the best of the authors' knowledge, this is the shortest adult achondroplastic patient ever reported to undergo such major abdominal surgery under general anaesthesia. The anaesthetic implications in patients with achondroplasia are reviewed in this case report.

Alcohol ablation is an accepted technique for the management of arteriovenous malformations. It is preferred due to the unique property of absolute alcohol to cause complete ablation and prevention of revascularisation. However, this technique is associated with multiple complications which may lead to patient morbidity. Here the case is presented of a female patient with scalp arteriovenous malformation who underwent alcohol ablation and developed supraventricular arrhythmia accompanied with haemodynamic instability and intravascular haemolysis in the postoperative period.

A 60-year-old patient suffering from pemphigus vulgaris for the past year was admitted to the emergency ward for fracture neck of femur. She also presented with lesions involving oral mucosa, back, inframammary and genital areas which were in partial remission. In hospital she was diagnosed with hypertension and was put on anti-hypertensives. Special attention was paid during positioning for surgery, administration of regional anaesthesia and placement of the intravenous line as well as monitoring devices. General anaesthesia was avoided in the presence of partially active oral lesions. Combined spinal-epidural anaesthesia was administered using bupivacaine-clonidine mixture. No haemodynamic complication was observed with 30 µg of clonidine intrathecally and no skin lesion occurred at the site of injections or Tegaderm application.

The failure of an epidural catheter after initially functioning well may be due to kinking, knotting or epidural catheter lumen blockage. The presence of blood in the epidural catheter is usually due to the catheter's traumatic placement or to intravascular migration. We describe an unusual cause of blood in the epidural catheter.